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NASA NTRS1986

Far infrared observations of crab-like supernova remnants

Using the Infrared Astronomy Satellite (IRAS) data, an investigation was begun of the far infrared properties of Crab-like supernova remnants and other synchrotron nebulae. Both the co-added scanning data and, where available, pointed observations were examined. To date infrared emission was found from two Crab-like remnants: G24.7+0.6 in which the infrared source near the center of the object was shown to be a compact HII region with EM greater than or approximately 10 to the 7th pc/cm(6); and G0.9+0.1 where a marginal detection of a 25 micron source coincident with the remnant core was used to set limits on the energetics of this synchrotron nebula. Further work, in progress under a second year of this program, should yield additional information concerning the distribution of initial pulsar spin periods and the evolution of synchrotron nebulae.

Helfand, David J.↗
NASA NTRS1986

The 2 micron spectrum of NGC 6240 - Evidence for more than a starburst

The exceptionally luminous interacting galaxy NGC 6240 has been studied with infrared spectroscopy and photometry. Emission lines of molecular hydrogen and the Paschen-alpha line of ionized hydrogen have been detected. Broad-band 10 micron and 20 micron emission has also been observed. Combined with previous optical spectroscopy and results from IRAS, the observations show that NGC 6240 cannot be explained along the lines of a superstarburst of massive stars such as seen in M82. It may be more easily understood in terms of an active nucleus similar to Seyfert galaxies.

Depoy, D. L.↗
NASA NTRS1986

Prospecting for planets in circumstellar dust - Sifting the evidence from Beta Pictoris

IRAS and near-IR coronographic data for the A5V star Beta Pic are analyzed for evidence of planetary formation. The light scattered from the central star in the system is integrated along the distance to the star to determine the disk magnitude at various distances from the star. A modified gamma distribution is applied to evaluate the scattering coefficient to test a hypothesis that the inner 30 AU of the disk has been swept out by planets. The scattering from the region around Beta Pic is compared with scattering around other A5V stars. Finally, the IR data at 0.89 micron is compared with scattering at the coronograph wavelengths. No evidence is found to support the hypothesis of clearing in the inner disk, although large particle densities can be found very close to Beta Pic. The study illustrates the effectiveness of using scattered light and IR data to discover and characterize matter distributions circumstellar disks.

Diner, D. J.↗
NASA NTRS1986

MID-IR emission of the interstellar medium

IRAS observations of the local interstellar medium and the galactic plane are presented; for all components, the radiation observed at 12 microns represents a large fraction of the far-IR emission. The 12/25 microns color of the diffuse IR emission of the galactic plane increases from the inner to the outer parts while the 60/100 microns ratio decreases, a color-color anticorrelation also observed for giant H II regions. The implications of these observations are discussed.

Boulanger, F.↗
NASA NTRS1986

The infrared astronomical satellite asteroid database

The creation, maintenance, and distribution of the set of ground-based observational data being used to help calculate the diameters and albedos of asteroids observed by IRAS during the sky survey of February-November 1983 are discussed in a status report. The database comprises orbital elements, absolute magnitudes, UBV colors, thermal radiometry, light-curve parameters, and taxonomic classifications; supplementary files include eight-color photometry, spectrophotometry, polarimetry, JHK observations, proper elements, discovery data, occultation diameters, radar characteristics, and references. Distribution in machine-readable and hard-copy formats and maintenance of the database by incorporating new data as they are published are planned.

Tedesco, E. F.↗
NASA NTRS1986

The Oort cloud in transition

The evolution of theoretical and empirical models of the Oort cloud (OC) since it was first proposed by Oort in 1950 is traced, and the main features of current models are discussed, in a general review. Consideration is given to work on the classical OC (Monte Carlo simulations of OC evolution, population and mass estimates, and OC perturbation by passing stars and giant molecular clouds), models of a massive inner OC (simulations of planetesimal-swarm evolution in the Uranus-Neptune zone and IRAS observations of circumstellar dust shells), evidence for random and/or periodic comet showers, and the possible role of the Galactic missing mass. The current OC model comprises an almost spherical outer (10,000-100,000-AU) cloud of mass 7-8 earth mass and population (1.4-2.3) x 10 to the 12th, and a flat disklike inner (40-10,000 AU) cloud of mass 100-200 earth mass and population (1-10) x 10 to the 13th.

Weissman, P. R.↗
NASA NTRS1986

Extended far-infrared emission associated with mass outflows from young stars: L1551 IRS 5

Coadded IRAS survey data have been examined in the L1551 region. Extended low-surface-brightness 60 and 1200-micron emission is aligned with the molecular outflow from L1551 IRS 5. The morphology and the uniform surface brightness and color temperature of the IR emission suggest that the wind from IRS 5 is the source of this emission. It is suggested that radiative heating of grains by photons generated at the stellar wind/cloud interface is a major contributor to the extended infrared emission.

Edwards, S.↗
NASA NTRS1986

R Coronae Borealis stars and planetary nebulae

IRAS observations of R Coronae Borealis type stars (R CrB's) suggests that a subset of these is inside planetary nebulae (PNs). In most cases, the PN is confirmed by the finding of a visible nebula around the star. These nebular R CrB's are identified as being the results of a final helium shell flash on the central star of old PNs. The majority of the R CrB's formed after the coalescence of a binary consisting of CO and He white dwarfs. Also presented in this paper are the results of a survey of 52 R CrB's. The normal R CrB's have power-law spectra which imply that the grain absorption coefficient varies linearly with frequency. It is estimated that R CrB's eject about 300 clouds per year, each of which subtend an angle of about 30 sq deg.

Schaefer, B. E.↗
NASA NTRS1986

Spectral energy distributions of active galactic nuclei between 0.1 and 100 microns

The 0.1-100-micron line-free spectral energy distributions of 29 AGN are characterized by fitting simple models to data from IRAS and IUE observations and ground-based NIR and optical spectrophotometry. The data are presented in tables and graphs and discussed in detail. It is found that nuclear dust does not play a major role in most of the Seyfert 1 galaxies and QSOs, which can be described by a model with four spectral components.

Edelson, R. A.↗
NASA NTRS1986

Active extragalactic sources - Nearly simultaneous observations from 20 centimeters to 1400 A

IRAS, IUE, and ground-based optical, NIR, mm and submm, and radio observations obtained mainly on Apr. 9-23, 1983, are reported for 19 active extragalactic sources and eight control sources. The overall spectra of the compact active sources are shown to be well represented by continuous-curvature functions such as parabolas. The spectra are found to be consistent with models involving continuous particle injection (with synchrotron losses) or first-order Fermi acceleration (with escape and synchrotron losses), but not with models using relativistic Maxwellian electron distributions.

Landau, R.↗
NASA NTRS1986

Discovery of an infrared-loud quasar

The IRAS source 13349 + 2438 is a quasar with a redshift of z = 0.107, broad (15,000 km/s) emission lines and a luminosity of 2.7 x 10 to the 12th solar luminosity, emitted mostly between 4.8 and 12 microns. The object, a weak radio source, is the first previously unidentified quasar selected through its infrared emission and is the prototype radio-quiet, infrared-bright quasar. A dusty interstellar medium may be responsible for the infrared emission as well as for quenching the visual emission and attenuating the radio emission from the central energy source.

Beichman, C. A.↗
NASA NTRS1986

Infrared spectra of rotating protostars

Earlier calculations of the infrared emission expected from stars in the process of being made are corrected to include the most important observable effects of rotation and generalized. An improved version of the spherical model of a previous paper is developed, and the corresponding emergent spectral energy distributions are calculated for the theoretically expected mass infall rate in the cores of cool and quiescent molecular clouds. The dust grain opacity model and the temperature profile parameterization are improved. It is shown that the infrared spectrum of the IRAS source 04264+2426, which is associated with a Herbig-Haro object, can be adequately represented in terms of a rotating and accreting protostar. This strengthens the suggestion that collimated outflows in young stellar objects originate when a stellar wind tries to emerge and reverse the swirling pattern of infall which gave birth to the central star.

Adams, F. C.↗
NASA NTRS1986

The SIRTF mission

This paper describes the scientific and technical background and prospects for the Space Infrared Telescope Facility (SIRTF). SIRTF is a cryogenically-cooled, one meter-class space telescope which will be operated by NASA as an observatory for infrared astronomy, in the mid-1990's. SIRTF will provide detailed studies of even the faintest IRAS sources, important new capabilities for the study of known astrophysical phenomena, and the potential to make new and unexpected discoveries about the nature of the universe. The long-life SIRTF mission has undergone intensive review by the SIRTF Science Working Group, which was selected in mid-1984. This paper presents the outcome of that review process and describes the SIRTF program as it is now envisioned. Particular emphasis will be placed on the choice of orbit for SIRTF, the SIRTF scientific performance requirements, and the baseline design concept for the SIRTF facility and mission.

Werner, Michael W.↗
NASA NTRS1986

The Draco cloud as a matrix of potential protostars

The Draco molecular cloud is inbound at a z distance of a few hundred parsecs, according to previous observations. IRAS Point Source Catalog data for a 36 sq deg area that includes most of the cloud and a comparison area around it are tabulated, illustrated, and discussed. The sources are classified as 56 unidentified, 38 identified extragalactic objects, and 44 identified stars. The unidentified and unresolved 100 micron sources appear to be globule-like clumps that are candidates for producing protostars, although the data cannot demonstrate currently accreting protostars in the globules. An undetermined percent of 100 micron sources may be artifactual, but only a small percent of them may be galaxies because of the adherence to the Draco cloud. Sources detected also at 60 micron or only at 60 micron do not adhere to the cloud and are probably galaxies. Unless artifactual the unidentified and unresolved 100 micron sources may provide considerable new information about the cloud components and therefore about potential star formation in a new class of sites and origins. Six unidentified sources have 12-25 micron stellar spectral distributions, but neither they nor the identified stars have 12-25 micron spectra characteristic of T Tauri stars.

Johnson, Hugh M.↗
NASA NTRS1986

RV Tauri stars as post-asymptotic giant branch objects

RV Tau stars are rare, luminous pulsators of spectral types F, G, and K. Analysis of the IRAS data shows that the mass-loss rates from RV Tau stars have apparently significantly decreased during the past 500 yr. It seems likely that these stars have just evolved from the phase of rapid mass loss, characteristic of the last stages of the asymptotic giant branch (AGB). The birthrate of RV Tau stars in the solar neighborhood is about a tenth of the birthrate of all planetary nebulae, and this is consistent with the view that we are witnessing the subset of stars undergoing post-AGB evolution that are low mass and at least in some cases of low metallicity.

Jura, M.↗
NASA NTRS1986

An unbiased survey for high-velocity gas in the Monoceros OB1 molecular cloud

In order to make an unbiased survey for high-velocity gas in a single molecular cloud, a sensitive and uniformly sampled map of CO (J = 1-0) emission over a large fraction of the Mon OB1 (NGC 2264) molecular cloud was obtained. High-velocity line wings were detected on profiles over about 10 percent of the region surveyed. Complete maps of the 12, 25, 60 and 100-micron far-infrared emission from the Mon OB1 cloud were constructed as well by coadding the appropriate IRAS survey fields.

Margulis, Michael↗
NASA NTRS1986

Continuum emission in active galactic nuclei; Proceedings of the Workshop, Tucson, AZ, January 11-14, 1986

Papers are presented on IRAS observations of active galactic nuclei, 0.3-100 micron continua of Seyfert 1 galaxies, the diverse soft X-ray slopes of QSOs, and the continuum variability of the optically-active radio-quiet quasar GQ Comae. Also considered are the polarization signatures of accretion disks in active galactic nuclei, X-ray spectra of BL Lacertae objects, diffusive shock acceleration and quasar variability, and radio-optical broadband spectra and variability of quasars. Other topics include the radio properties of optically selected Seyfert galaxies, and the structure of the emission region in blazars.

Sitko, Michael L.↗
NASA NTRS1986

A multiwavelength investigation of the supernova remnant IC 443

Multiwavelength observations of the supernova remnant IC 443 at radio, infrared, optical, ultraviolet, and X-ray wavelengths are presented. This morphological study of IC 443 presents a detailed picture of an adolescent supernova remnant in a multiphase interstellar medium. Radio observations show that better than 80 percent of the continuum emission at 18 cm is in a large-scale (greater than 18 arcmin) component. Decomposition of the infrared data shows that radiatively heated dust, shocked blackbody dust emission, and infrared line emission are all important components of the observed IRAS fluxes. The morphology of the IC 443 region is consistent with a supernova blast in an interstellar medium with a nonuniform distribution of clouds. The bright northeast rim and the great extent of the remnant to the southwest are most easily explained by a cloud filling factor which is greatest in the northeast and falls off toward the southwest.

Mufson, S. L.↗